Osteoporosis is a disease involving considerable socio-economic implications in that it leads to hip fractures, vertebral fractures which cause severe pain and immobility and often result in surgery. The diagnostic test of choice for determining osteoporosis (prior to the present invention) is bone densitometry using a dual x-ray beam device, though it is also possible to use tests such as computed tomography CT and magnetic resonance imaging and/or ultra-sound measurements. None of these processes is of wide spread use due to the associated high cost of testing.
Dual energy x-ray absorption (DXA) and quantitative computed tomography (QCT) measure the electron density of bone which is almost entirely due to its calcium content. These procedures provide a measure of bone mass and thus an indication of whether the patient is suffering from osteoporosis since in osteoporosis there is a proportional loss of both matrix and material.
Quantitative ultra-sonography (QUS) is currently being investigated for use in the diagnosis of osteoporosis. This technique is based on the speed of transmission of the sound waves or signal transmitted by the bone.
The concept of using acoustic emissions for detecting bone damage such as cracks or for detecting the degree of wear in a joint has been described in German patent 442451 A1 published on Feb. 12, 1995. This describes applying a load to a bone and measuring the acoustic emission from the bone to assess the strength in the individual's bones being examined. The acoustic emission technique described in that German patent is used for determining the individual breaking load of human bone under mechanical load by evaluating the acoustic signals that are generated during crack formation or as generated in joints during movement. The patent states that for detecting cracks, analysis of the signal should be based on the peak amplitude of the signal generated and that for determining joint wear, i.e. during friction such as occurs in joints, the analyses should be based on the root mean square of the signal generated.
U.S. Pat. No. 4,836,218 issued Dec. 17, 1991 by Gray et al. describes a method of determining joint disorders by measuring acoustic emissions of the joint correlated with the position of the joint. (See also WO85/04564 published Oct. 24, 1985.)
U.S. Pat. No. 4,437,473 describes a technique for evaluating joints by detecting sounds generated by moving of the joints, in particular, analyzing acoustic emissions extending into the subsonic frequency ranges was found to be important to these diagnoses.
U.S. Pat. No. 4,823,807 issued Apr. 25, 1989 to Russell et al. is similar to technique of U.S. Pat. No. 4,437,473 discussed above in that it describes a method of examining for joint damage by defining an angle between two bones, angularly moving the bones while sensing the acoustic signals emitted from the joint between the bones during the relative angular movement and while applying a preselected resistance to the angular movement thereby stressing the joint.
Bones have been examined in-vitro and the differences identified between normal and osteoporotic (chemically digested) bones using acoustic emission techniques. See Hasegawa et al. "Failure Characteristics of Osteoporotic Vertebral Bodies Monitored by Acoustic Emission", Spine 1993, column 2314-2320 and/or Hasegawa et al "Mechanical Properties of Osteopenic Vertebral Bodies Monitored by Acoustic Emission", Bone 1993, 37-743. The use of acoustic emission to determine osteoporosis or the attempt to determine osteoporosis in vitro obviously is of no value in diagnosing osteoporosis in a patient.
The present diagnostic tests for osteoporosis are quite expensive and thus are not widely used as screening tools. The present invention provides an inexpensive, simple to use evaluation system for measurement of osteoporosis. Such testing if performed more routinely would result in treatment for the disease using drugs available for the purpose such as the biphosphonates, for the overall benefit of the patient and society.